This invention relates to gas burners in general and more particularly to a gas burner for the interior heating of hollow rolls.
If a gas burner is used for the heating of a roll, the burner nozzle tube typically extends through the interior of the hollow roll and is supplied from the end with gas, in particular a fuel gas/air mixture. The burner nozzles are mounted on the outside of the burner nozzle tube with relatively little mutual longitudinal spacing in a lengthwise region of the burner nozzle tube which corresponds approximately to the width range of the web to be processed. Since the burner nozzle tube is stationary and the hollow roll rotates about the burner nozzle tube, temperature equalization is obtained in the circumferential direction. However, the temperature equalization at the ends of the row of burner nozzles is a problem if their length does not agree with the width of the web. If burner nozzles are still in operation outside the edge of the web in the interior of the hollow roll, the edge region of the hollow roll is heated more than the region in the middle because there is no longer a web opposite the edge region which removes heat continuously. Therefore, the temperature rises at the edge. If, however, the region covered by the burner nozzles is narrower than the web, the edge of the web removes heat on the outside in a region in which no heat is replenished from the inside and, in this case, the temperature drops toward the edges of the web.
It is, thus, an object of the present invention to develop a gas burner having active length, i.e., the region in which operating burner nozzles are present, which can readily be adapted to changing web widths.